Interlayer coupling driven rotation of the magnetic easy axis in MnS e 2 monolayers and bilayers

Interlayer coupling plays a critical role in tuning the electronic structures and magnetic ground states of two-dimensional materials, influenced by the number of layers, interlayer distances, and stacking order. However, its effect on the orientation of the magnetic easy axis remains underexplored. In this study, we demonstrate that interlayer coupling can significantly alter the magnetic easy-axis orientation, as shown by the magnetic easy axis of monolayer $1T\ensuremath{-}\mathrm{Mn}{\mathrm{Se}}₂$ tilting 67\ifmmode^\circ\else\textdegree\fi{} from the $z$ axis, while aligning with the $z$ axis in the bilayer. This change results from variations in orbital occupations near the Fermi level, particularly involving nonmetallic Se atoms. Contrary to the traditional focus on magnetic metal atoms, our findings reveal that Se orbitals play a key role in influencing the easy-axis orientation and topological Chern numbers. Furthermore, we validate our conclusions by changing stacking orders, introducing charge doping, applying in-plane biaxial strains, and substituting nonmetallic atoms. Our results highlight the pivotal role of interlayer coupling in tuning the magnetic properties of layered materials, with important implications for spintronic applications.